A procedure was developed for preparing uniform fecal samples for LSC counting and study of fecal metabolites. The procedure requires milling of a rat or monkey feces sample with anhydrous Na2SO4 in a stainless steel ball mill. The fine off-white flours that result are passed through a fine wire sieve (18-8 stainless steel wire, 30 holes/inch). This sieving increases homogeneity by removing traces of unground material and dietary fiber. Digestion of samples with NaOH and counting total 14C in dioxane-toluene-naphthalene with Cab-O-Sil (DTN-C) gave reproducible recoveries. This procedure was adequate for 0.25 g and 0.5 g samples but inadequate for 1.0 g samples. In a study of 7 solvent/digestants (1) Soluene, (2) NaOH and (3) Protosol extracted the most dpm (14C) from feces samples and showed the best reproducibility. Protosol and Soluene digests counted as efficiently in Biofluor as in DTN-C. Ten replicate Soluene digests in Biofluor and 10 replicate NaOH digests in DTN-C showed mean % recoveries which matched well (NaOH, 40.6 + or - 1.0 SD; Soluene, 41.3 + or - 1.35 SD). Combustion assays for total 14C gave recoveries that agreed well with values obtained by digestion in NaOH, Soluene, and perchloric acid - H2O2. One gram aliquots of 4 milled feces samples were extracted sequentially 3 times with THF and extracted once with Soluene.